For purposes of telephone communications, a geopolitical area, such as the United States, is divided into a plurality of contiguous, non-overlapping districts, called exchanges, each of which is served by a local telephone company. In telephony parlance, the exchanges are also referred to as Local Access Transport Areas (LATAs). Telephone calls originating and terminating within the same exchange, referred to as intraexchange calls, are generally handled end-to-end by a local, intraexchange, telephone company. Calls originating within one exchange or in a foreign country and terminating in a different exchange or in a foreign country, referred to as interexchange calls, are handled at each end by the intraexchange company that services the originating or the terminating exchange, and the calls are carried between the intraexchange companies by one or more interexchange carriers.
A plurality of alternative interexchange carriers have come to be available to callers to carry their interexchange calls. It is therefore necessary to provide callers with the capability of selecting interexchange carriers, and to provide interconnection between callers and the selected interexchange carriers. Furthermore, it is desirable to provide interconnection between any caller and any interexchange carrier on the same type of basis.
The conventional scheme of providing interconnection between callers and carriers has not completely satisfied the objective of providing interconnection to all carriers on an equal basis. Traditionally, to have their interexchange calls completed and carried by one interexchange carrier, callers have merely had to dial the number of the called party. However, to have their interexchange calls carried by other interexchange carriers, the callers have had to dial access codes assigned to those carriers. Dialing of the access code has provided the callers with connection to the selected carrier, and the callers then have had to dial a personal identification code and only then the number of the called party, to have the call completed.
Additionally, an intraexchange telephone company has typically been able to transfer interexchange calls to one interexchange carrier over various routes, as a function of certain parameters that are associated with each call, such as the class of service of the call-originating equipment and the called number. Alternative interexchange carriers have generally not been provided with this capability in an efficient manner and they have had to receive calls of all types over a single type of route.
Furthermore, the intraexchange telephone companies have conventionally been able to keep various records, and to perform various servicing activities, on calls routed via an interexchange carrier, and therefore the protocol for communications between switching offices of the local telephone companies and of the carrier has not had to provide for transfer of information necessary to make these records and to perform these activities. But the protocol has been found lacking in capabilities to communicate the requisite information from the local telephone companies to the carriers to enable the carriers to keep their own records on, and to provide services for, calls routed to them. And while conventionally a switching office could assume that information sent by it to a carrier office was properly received, a need has arisen for determining that sent information has actually been received. But the conventional interoffice communication protocol has been found lacking in capabilities for determining whether the carrier office has received the communicated information.